i highly recommend Samsung TCCD based memory for an A64 platform. the on-die memory controller of the A64s has been known to be very picky about RAM. Corsair, OCZ, PQI, Patriot, GSkill all produce TCCD based memory.
if you're mainly doing video/photo work, you'll see the added benefit of 2GB of RAM over 1GB but i would still try and go with known/proven brands (not only for performance reasons, but for warranty/support reasons). you should also check the Asus site for the list of approved RAM for your motherboard. i have 2 Asus mobos (one 754 pin A64 and the other 939 pin A64). i use Corsair in one (though it's not ideal at all) and OCZ in the other.
The OCZ Platinum Revision 2 PC3200 ram is highly regarded as the best RAM (regardless of overclocking or not) for the A64 platform. OCZ also has THE BEST customer support in the biz (currently).
@crustyteacup: the app your thinking of is Memtest 86 and runs right from boot (before loading windows) off a floppy or CD. it's used to test the stability of RAM to see if it can run at certain speeds and timings, but also to check for faulty sticks (which definitely are around).